1. Field of the Invention
This invention relates to high temperature heating vessels and in particular to a modular lid construction for a glass melting furnace.
2a. Technical Considerations
One type of glass melting process entails depositing pulverulent batch materials into a pool of molten glass maintained within a tank type melting furnace and applying thermal energy until the materials are melted into the pool of molten glass. The melting tank conventionally contains a relatively large volume of molten glass so as to provide sufficient residence time for currents in the molten glass to effect some degree of homogenization before the glass is discharged to a forming operation. These recirculating flows in a tank type melter may result in inefficient use of thermal energy. Conventional overhead radiant heating is inefficient in that only a portion of its radiant energy is directed downward towards the material being melted.
As an alternative to conventional tank type glass melting furnaces as described above, U.S. Pat. No. 4,381,934 to Kunkle and Matesa discloses an intensified batch liquefaction process in which large volumes of batch are efficiently liquefied in a relatively small liquefaction vessel. This type of process, particularly when using intensified heat sources, produces relatively small volumes of high temperature exhaust gas. The heat from this exhaust gas can be recovered and used to directly heat a batch stream feeding the liquefaction vessel so as to improve the overall efficiency of the process.
In a heating operation, the high temperature may adversely affect the heating vessel. Heating processes may cause portions of the material being heated to vaporize. These vapors may be corrosive and corrode exposed inner surfaces of the vessel. The corrosion may be further accelerated by the high temperature environment within the heating vessel.
In a glass batch melting process as taught in U.S. Pat. No. 4,391,934, the degradation of the exposed surface of the liquefaction vessel's lid is further aggravated by the high temperature exhaust gas from the burner, that circulates through the vessel. Not only may the high temperature exhaust combine with the vaporized batch materials but also with particulate matter within the vessel. The entrained particulates may have an abrasive action, which when combined with the high temperature gas stream corrodes and erodes the lid's inner surfaces.
Due to the high temperature and corrosive effects of the gas stream within the vessel as well as any erosion effects from the entrained particulates, the lid or portions of the lid must be periodically repaired or replaced to correct any excessive wear at its inner surface. It would be advantageous to have a lid design wherein selected portions of the lid can be removed as a single unit with minimal effect on the remaining portion of the lid or the heating process.
2b. Patents of Interest
U.S. Pat. No. 180,028 to Holley teaches an arch furnace roof construction wherein cooling pipes are positioned between adjacent rows of refractory block. Each block is channeled to receive one-half of the pipe cross-section so that the pipe is fitted between adjacent blocks. The pipes can also be used to form tension members to support blocks along a downwardly curved configuration rather than in an arch type arrangement.
U.S. Pat. No. 1,109,553 to Slick teaches furnace construction wherein refractory bricks are carried by hollow, water cooled girders extending up between and separating the upper parts of the rows of bricks. The girders span the width of the furnace and include enlarged shoulder portions that are received by corresponding recesses in the bricks. The bricks supported by adjacent rows of girders can be formed to support additional bricks not directly supported by the girders.
U.S. Pat. No. 1,724,340 to Charles teaches a smelting furnace construction wherein the bricks in an arched roof are water cooled. The bricks are hollow and include a metal cylinder container therein. Coolant is pumped into the cylinder, circulated therethrough and removed. The coolant inlets and outlets of each cylinder are connected to common overhead cold water and hot water headers, respectively.
U.S. Pat. Nos. 2,699,740 to H. W. Webber and 2,753,711 to H. G. O. Webber each teach suspended roof construction wherein a plurality of bricks are interconnected to and supported by a carrier which in turn is supported by an overhead frame. In U.S. Pat. No. 2,699,740 the carrier is a specially shaped wide flange section. The upper flange wraps around the lower flange of an overhead frame and its lower flange supports a pair of bricks that are interconnected with other bricks to form the roof structure. In U.S. Pat. No. 2,753,711 the upper section of a carrier brick is supported by a hanger beam while its flared lower section supports a set of interlocking brick.
U.S. Pat. No. 4,319,908 to Sensi teaches a float glass forming chamber with a roof comprised of suspended refractory slabs. Hanger rods extend through the roof slabs and are affixed at their lower ends to horizontal plates on which the weight of the slab rests. Each rod is affixed at its upper end to an overhead support structure. The number of joints and non-planar interior surfaces are reduced to suppress condensation and drippage of volatile materials within the chamber.
U.S. Pat. No. 4,340,412 to May teaches a float glass forming chamber with an externally supported roof. The roof is comprised of relatively large precast refractory slabs suspended from above by a hanger arrangement external to the forming chamber enclosure. The support arrangement is adapted to engage the top sides of the slabs so as to avoid support members which extend through or nearly through the roof elements.
U.S. Pat. No. 4,434,495 to Tomizawa et al. teaches a cooling pipe structure for arch furnaces. A plurality of cooling pipes are embedded in the refractory and are supported by a pair of support pipes. The support pipes recirculate coolant back and forth between the support pipes through the cooling pipes.
U.S. Pat. Nos. 4,424,756 and 4,475,470 to Merkle teach a suspended roof for an industrial furnace. Each hanger is recessed in the side of a pair of adjacent carrier bricks. Each carrier brick, in turn, supports two filler bricks so that a single embedded hangar supports six bricks: two carrier bricks and four filler bricks. The hangers are hung from telescoping tubes which may be retracted to remove successive groups of bricks. The tubes are hung by rods or wires from an overhead cross beam to support the entire roof structure.
In the previously discussed art, there are no provisions made for removing a single insulating unit and its cooled support structure from a furnace roof without requiring additional blocks to be removed with it or requiring the heating operation of the furnace to be shut down. Each provides in one form or another (a) that the units in the roof are interconnected so that the removal of one unit requires the removal of the adjacent units or (b) that the unit hangers are connected to common supports that require the removal of plurality of hangers prior to reaching as interior block unit or (c) that a plurality of units are all supported by a common hanger and removal of an individual interior unit would require the removal of the units leading to the interior unit or removal of the entire hanger along with all the units.